我用数组创建了JButton循环，但它不起作用

Question

我想按循环创建按钮

• 1 2 3
• 4 5 6
• 7 8 9

但是当我写代码的时候，按钮有array2D

private JButton cells[][];

// Constructor
public SliderGameFrame() {
    JPanel panel = new JPanel();
    this.add(panel);
    for (int i = 1; i <= cells.length; i++) {
        for (int j = 1; j <= cells.length; j++) {
            cells[i][j] = new JButton(" " + i);
            panel.add(cells[i][j]);
        }
    }
}

它不工作，错误消息是java。lang.NullPointerException

Answer 1

更改：

    for (int i = 1; i <= cells.length; i++) {
        for (int j = 1; j <= cells.length; j++) {

进入：

for (int i = 0; i < cells.length; i++) {
    for (int j = 0; j < cells.length; j++) {

二维数组的索引从0到维1开始